The known methods of weft thread insertion into the shed of an air-operated jet loom, as disclosed, e.g., in U.S. Pat. No. 3,911,968 or GB 1,333,948 use a profile swinging loom reed with a direct pick channel, and a pneumatic system consisting of a main pick jet and a series of geometrically arranged ancillary jets for controlling the weft thread during the weaving process. The improvement of the efficiency of the ancillary jets is directed in particular to increase the reliability of the pick of the weft thread thrown into the shed of the warp threads, to reduce the consumption of air and, as the case may be, of electric power as well, and to increase the pick speed of the weft thread. In general terms, the dominant aim is to achieve a top-quality weft thread pick, this quality being under the existing circumstances a fundamental criterion having a decisive influence both on the economy and on the quality of the weaving process.
The known device for inserting the weft thread into the shed of an air-operated loom, schematically shown in FIG. 1, contains a profile loom reed P in which there is provided, approximately in the middle between the upper and the lower weave of the system of flat profile reed dents PT, free space for the weft thread pick, referred to as pick channel K. The open side of the pick channel K is situated in the direction of the tangent to the periodical swinging movement of the batten B in which the loom reed P is fixed. During the forward movement of the loom reed P towards the cloth, the rear closed side of the pick channel K carries the weft thread, and in the tangent direction of the movement of the batten B beats-up the weft thread to the cloth face.
The action of the pneumatic system of the loom creates a stream of the carrying medium imparting its motion energy to the weft thread being picked in the pick channel of the profile loom reed. This imparting action takes place only in a definite interval of the operation cycle of the loom when the area of the pick channel is not covered with warp threads or, in other words, when the shed is open. This time interval is often referred to as picking angle, if its magnitude is expressed in grades indicating the amount of turning motion of the main shaft of the loom. The performance of the loom is then directly proportionate to the magnitude of the picking angle and to the speed of the weft thread picking.
The speed of the weft thread picking depends on the quality of the speed field of the carrying substance, e.g. of air, in the pick channel K, produced by the ancillary jets T, situated at a predetermined interval along the loom reed P in the direction of the loom width. The quality of the speed field of the carrying substance is influenced by the concrete form of the ancillary jet T, outlet coefficient (factor) dispersion, etc., and also by the location of the outlet aperture V of the ancillary jet T, i.e., by the position of the axis OV of the outlet aperture, corresponding to the axis of the stream of the carrying substance streaming out, with respect to the axis OK of the pick channel K of the loom reed P. Under these conditions, the ancillary jets T are seated under the shed axis and are fixed to the batten B of the loom in such a manner that during the periodical swinging movement of the loom reed P carrying batten B they do not prevent the picked weft thread from being beaten-up to the cloth face and bound by the warp threads.
To further define the influence of this arrangement of the air-operated jet looms with profile loom reeds used, the following facts about the action of the carrying substance, e.g., of an air stream, on the weft thread under the pick conditions are provided.
The relations describing the action of the air stream on the weft thread immersed in, and surrounded by, the air stream, lead to the conclusion that the magnitude of the resultant of the vector sum of the outer forces acting in a certain direction on a length element of the weft thread is a function of the flow momentum. The latter being the difference between the momentum of the carrying substance leaving the surface area of the weft thread surrounded by it, and the momentum of the carrying substance entering into contact with the surface area of the weft thread.
The outer forces are: the pressure force, uniform in the whole surrounding area and therefore producing a zero effect; the flow momentum introduced from the outside under the action of the loom pneumatic system exerted on the weft thread surrounded by the air flow, in connection with the force of gravity acting on the weft thread; and the force of gravity acting on the carrying substance, which is so small as to be negligible.
In the real pick, the action of the air stream is a very complicated phenomenon because the air stream is neither constant in time nor laminar. Due to this, the position of, above all, the weft thread point carried by the air stream in the pick channel is not constant; further, in the pick interval, the loom reed moves together with the loom batten.
In the known ancillary jets T used in air operated jet looms equipped with a direct pick channel K in the profile loom reed P, the axes OV of the outlet apertures V of the ancillary jets T form an angle with the axes OP, the latter being perpendicular to the longitudinal axis of the ancillary jet T passing through the center of the outlet aperture V. This parameter, intrinsic to every ancillary jet T, is referred to as the elevation angle e. By turning the ancillary jet T about its longitudinal axis, the angle e between the air stream and the loom reed P can be modified. The adjustment in height of the position of the outlet aperture of the ancillary jet T in the direction of its longitudinal axis is carried out with reference to the contour of the pick channel K of the loom reed P.
To sum up briefly, the air stream flowing out of the outlet aperture V of the ancillary jet T acts in a direction forming a space angle .mu. with the axis OK of the pick channel K of the profile loom reed P. The force of the air stream acting in this direction can be resolved into components arranged in three-dimensional orthogonal coordinate system in which one component acts in the weft thread axis whose direction is, in the currently used version of pneumatic looms, broadly identical with the axis OK of the pick channel K in the profile loom reed P. A second component acts not in the weft thread axis, but instead, tends to push the weft thread to the dents PT in the rear section of the pick channel K of the profile loom reed P. This component is summarily counteracted by a reaction force trying to push the weft thread farther from the reed dents PT. This reaction force is generated, for instance, by the air stream between the dents PT of the loom reed P due to the motion of the loom reed P or by the action of the air particles of the carrying substance when rebounding from the dents PT of the loom reed P, etc. A third component, here acting vertically, depends on the magnitude of the above mentioned elevation angle e of the outlet aperture V of the ancillary jet T. This component is counteracted by the gravitational force due to the weft thread mass, and by the reaction force due to the stream particles of the carrying substance rebounding from the upper nose-like lug of the profile dents PT constituting the pick channel K of the loom reed P.
It is a general aim in the design of such machines to place the ancillary jet T with respect to the pick channel K so as to ensure that the force component acting in the weft thread axis is maximal, while the nose-like lugs that are a part of the profile of the pick channel K adversely affect the formation of the speed field inside the pick channel K.
The drawbacks of the currently used arrangement in an air-operated jet loom with profile loom reed, with an approximately horizontal plane of the shed axis, with the beat-up perpendicular to the shed axis plane, and with ancillary jets mounted below the shed axis, are due to the fact that the air stream coming from the ancillary jet enters the pick channel at a space angle and acts fully in the upper part of the pick channel while its action in the lower part of the pick channel is less intense. The differentiation of the speed field in cross section is due to the difference of intensity of the action of the picking substance in the upper and the lower part of the channel.
Partly due to the force of gravity, the weft thread tends to move during the pick to the lower part of the pick channel where the carrying substance moves at reduced speed. This can reduce the instantaneous as well as the average pick speed of the weft thread and consequently, the loom performance. In the most disadvantageous case, the weft thread can even get out of the pick channel, with ensuing defects in the weaving process, because a section of the weft thread is at a given time interval not exposed to the action of the carrying substance and is woven-in as a loop.
The uneven composition of the speed field along the axis of the pick channel, representing a non-stationary speed field generated by the carrying substance in the pick channel of the loom reed, is characterized also by the values of the stream speed of the carrying substance along the axis of the pick channel. But these values are exposed to heavy fluctuations in function of the value of the length coordinate. Maximum values are reached (in the stream speed) at the entry spot of the free stream of the carrying pressure substance from the ancillary jet into the pick channel area. With the increasing value of the length coordinate, the speed in the direction of the channel axis decreases up to the section where the speed field is acted upon by the carrying substance from the next ancillary jet. The front part, or the point, of the weft thread that is the part which most needs to receive kinetic energy, moves during the pick through such sections of the pick channel where the speed of the carrying substance is mutually different. Due to this, the weft thread is not ideally stretched during the pick and, again in the most unfavorable case, is apt to create loops due to the fluctuating tensile strength. In the currently used arrangement of the ancillary jets and of the pick channel, the speed fluctuation in the direction of the longitudinal axis of the channel is due to a compromise made in choosing the elevation angle of the ancillary jet, the size of the outlet aperture of the ancillary jet, and the distance between the ancillary jets. The direction of the carrying substance stream being determined by the designated position of the ancillary jet on the batten of a loom, and possible changes increasing either the distance between the ancillary jets or the size of the outlet apertures cannot be successfully applied without prohibitive increase in the energy consumption. Other means intended to reduce the differences of the speed field composition along the axis of the pick channel, such as an ancillary jet fitted with a plurality of outlet apertures whose axes form an angle different from zero, geometrically defined, are not applicable. Thus, it can be stated that in the case of a single outlet aperture in the ancillary jet or in case of a plurality of outlet apertures with parallel axes, the carrying substance acts on the weft thread in the section between two ancillary threads locally, because in the known arrangement of the ancillary jets with respect to the pick channel the stream of the carrying substance cannot be determined otherwise than in the described manner.
An attempt to eliminate at least a part of the above described drawbacks is disclosed, for instance, in GB 2 060720, aiming at evening out the air stream along the length of the pick channel of the loom reed. To achieve this, at least some of the ancillary jets are mounted rotatably on their axes. Depending on their angular position there is created a more or less oblique component of the air stream carrying the weft thread.
Neither this solution, nor the other known ones have succeeded in eliminating the basic drawbacks due to the fact that the air stream from the ancillary Set enters the pick channel under a given space angle and the uneven distribution of the speed field in the cross section of the pick channel of the loom reed.
Another drawback consists in the fact that the existing devices for entering the weft thread into the shed on an air-operated jet loom with a profile reed have comparatively high moment of inertia, approximately equal to the sum of the product of their masses with the squares of distance of their centers of gravity from the axis of the swinging motion of the batten. Since the magnitude of the force effects acting on the batten of a loom is the product of the moment of inertia and of the angular acceleration, it is as a rule necessary, for keeping them under control, to make a compromise to the detriment of the pick angle value, thus reducing the machine performance.
The invention aims to eliminate many of the drawbacks of the known method of inserting the weft thread into the shed of air-operated jet looms with a direct pick channel in the loom reed and to create a device for carrying out the method intended to permit an increase in the function parameters of a loom.